Surgical sealing surfaces and methods of use

ABSTRACT

Various embodiments provide compositions that exhibit positive temperature coefficient of resistance (PTCR) properties for use in thermal interactions with tissue-including thermal sensing and I 2 R current-limiting interactions. Embodiments also provide tissue-engaging surfaces having PTCR materials that provide very fast switching times between low resistance and high, current-limiting resistance. One embodiment provides a matrix for an electrosurgical energy delivery surface comprising a PTCR material and a heat exchange material disposed within an interior of the matrix. The PTCR material has a substantially conductive state and a substantially non-conductive state. The heat exchange material has a structure configured to have an omni-directional thermal diffusivity for exchanging heat with the PTCR material to cause rapid switching of the PTCR material between the conductive state and non-conductive state. Preferably, the structure comprises a graphite foam having an open cell configuration. The matrix can be carried by tissue contacting surfaces of various electrosurgical devices.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit under 35 USC 119(e) of U.S.Provisional Patent Application No. 60/563,424 (Attorney Docket No.021447-002300US) filed Apr. 19, 2004, the full disclosure of which isincorporated herein by reference.

This application is also related to co-pending U.S. patent applicationSer. No. 10/032,867 (Docket No. 021447-000500US), filed Oct. 22, 2001,titled Electrosurgical Jaws Structure for Controlled Energy Delivery;U.S. patent application Ser. No. 10/351,449 (Docket No.021447-000100US), filed Jan. 22, 2003, titled Electrosurgical Instrumentand Method of Use; U.S. patent application Ser. No. 10/443,974 (DocketNo. 021447-000590US), filed May 22, 2003, titled Electrosurgical WorkingEnd with Replaceable Cartridges; U.S. patent application Ser. No.10/993,210 (Docket No. 021447-002310US), filed Nov. 18, 2004, titledPolymer Compositions Exhibiting a PTC Property And Methods ofFabrication; Provisional U.S. patent application Ser. No. 60/523,567(Docket No. 021447-000560US), filed Nov. 19, 2003, titledElectrosurgical Instrument and Method of Use; Provisional U.S. patentapplication Ser. No. 60/537,085 (Docket No. SRX-028), filed Jan. 16,2004, titled Electrosurgical Working End with Replaceable Cartridge;Provisional U.S. patent application Ser. No. 60/552,978 (Docket No.SRX-029), filed Mar. 12, 2004 titled Electrosurgical Instrument andMethod of Use; Provisional U.S. patent application Ser. No. 60/558,672(Docket No. SRX-030), filed Apr. 1, 2004, titled Surgical SealingSurfaces and Methods of Use; and U.S. patent application Ser. No.10/781,925 (Docket No. 021447-000810US), filed Feb. 17, 2004, titledElectrosurgical Instrument and Method of Use, the full disclosure of allof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of invention relates to electrosurgical systems for sealingtissue. More particularly embodiment related to a probe or jaw structurethat utilizes a polymeric positive temperature coefficient of resistance(PTC or PCTR) material in a sensing surface for control of thermalinteractions with engaged tissue in (i) thermal sensing interactions and(ii) in I²R current-limiting interactions with tissue.

2. Description of Background Art

Positive temperature coefficient (PTC) device are known in electronicindustries and are used as low power circuit protectors, thermal sensorsand as constant temperature heaters. FIG. 1A is an exploded view of acurrent-limiting device or thermistor 5 that has a polymeric PTCmaterial 10 sandwiched between a pair of foil electrodes (12 a and 12 b) and packaged within an insulator 14 (phantom view). FIG. 1B is aschematic view of a prior art current-limiting device or thermistor 5 ina circuit diagram showing that heating of the PTC material can limitcurrent flow to the load 16. FIG. 1C is a schematic view of a PTC device25 that consists of a constant temperature heating element for heatingsubject material 26 in contact with the device. In other words, thedevice of FIG. 1C comprises a PTC heater material that conducts heat tothe engaged subject material 26. The use of a PTC material as a heatingelement as in FIG. 1C was proposed in a surgical jaw structure in U.S.Pat. No. 5,716,366 to Yates et al.

In previous PTC devices, the polymeric PTC material consists of acrystalline or semi-crystalline polymer (e.g., polyethylene) thatcarries a dispersed filler of conductive particles, such as carbonpowder or nickel particles. In use, a polymeric PTC material willexhibit temperature-induced changes in the base polymer to alterelectrical resistance of the polymer-particle composite. In a lowtemperature state, the crystalline structure of the base polymer causesdense packing of the conductive particles (i.e., carbon) into itscrystalline boundaries so that the particles are in close proximity andallow current to flow through the PTC material via these carbon“chains”. When the PTC material is at a low temperature, numerous carbonchains form the conductive paths through the material. When the PTCmaterial is heated to a selected level, or an over-current causes I²Rheating (Joule heating), the polymer base material thus will be elevatedin temperature until it exceeds a phase transformation temperature. Asthe polymer passes through this phase transformation temperature, thecrystalline structure changes to an amorphous state. The amorphous statecauses the conductive particles to move apart from each other until thecarbon chains are disrupted and no longer conduct current. Thus, theresistance of the PTC material increases sharply. The temperature atwhich the base polymer transitions to its amorphous state and affectsconductivity is called its switching temperature T_(S).

As long as the base polymer of the PTC material stays above its T_(S),whether from external heating or from an overcurrent, the highresistance state will remain. Reversing the phase transformation allowsthe conductive particle chains to reform as the polymer recrystallizesto thereby restore multiple current paths (e.g., low resistance) throughthe PTC material.

Conductive polymer PTC compositions and their use as circuit protectiondevices are well known in the industry. For example, U.S. Pat. No.4,237,441 (Van Konynenburg et al.), U.S. Pat. No. 4,304,987 (VanKonynenburg), U.S. Pat. No. 4,545,926 (Fouts, Jr. et al.), U.S. Pat. No.4,849,133 (Yoshida et al.), U.S. Pat. No. 4,910,389 (Sherman et al.),U.S. Pat. No. 5,106,538 (Barma et al.), and U.S. Pat. No. 5,880,668(Hall) and EP-730 282 A2 (Unitika) disclose PTC compositions thatcomprise thermoplastic crystalline polymers with carbon particles orother conductive particles dispersed therein. The disclosure of each oneof these references is incorporated herein by this reference.

PTC devices are typically only employed in a passive role in anelectronic circuit, and “switch” when a voltage spike overheats thepolymeric material thereby causing its resistance also to spike.However, these devices do not consider the problem of rapid switchingfrom a conductive to a resistive mode. There is a need for conductivepolymer PTC compositions such as PTC composites which can switch in anextremely rapid, repetitive manner from a conductive to a resistivemode. There is also a need for PTC materials which have pixelated(localizable) switching across a surface of the PTC composition.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention provide polymeric positive temperaturecoefficient (PTC) devices and methods of use that allows for spatiallyresolved thermal interactions with targeted tissue. Specific embodimentsprovide polymeric PTC based device that exhibit highly nonlinear PTCeffects together with extremely rapid, repeatable switching at aselected switching temperature.

Many embodiment provide a polymeric PTC composition thermally coupledwith a heat exchange means for rapid transfer of heat from a surface ofthe PTC material that engage thermally treated tissue. The inventivepolymeric PTC device results in a highly stable current-limiting devicethat is capable of repeated cycling between an initial quiescentresistance and an operating resistance (or switching range).

One embodiment provides a matrix for an electrosurgical energy deliverysurface comprising a positive temperature coefficient of resistance (PTCor PTCR) material and a heat exchange material dispersed within aninterior of the matrix. The PTC material has a substantially conductivestate and a substantially non-conductive state. The heat exchangematerial has a structure configured to have an omni-directional thermaldiffusivity for exchanging heat with the PTC material to cause rapidswitching of the PTC material between the conductive state and thenon-conductive state. The matrix can be carried by tissue contactingsurface of various electrosurgical devices such as the jaw surface of aforceps or a like device.

The structure of the heat exchange material can be cellular, open cell,crystalline or otherwise non-amorphous. Preferably, the structurecomprises a graphite foam structure having an open cell or honey-comblike configuration. The foam structure can include a plurality ofthermally conductive filaments, such as carbon fibers which can moldedor otherwise incorporated into the matrix. The fibers can be oriented toconduct heat omni-directionally, bi-directionally or uni-directionallywithin the matrix and thus to and from portions of the PTC material. Inparticular, the conductive fibers can be configured to allow rapidconduction of heat from the surface of the matrix to adjacent orunderlying PTC material to allow rapid switching of that materialbetween conductive and non-conductive states during delivery of Rfenergy. The conduction and switching can be done at micron scale toallow micron size portions of the matrix to be in a conductive statesand adjacent portions to in a non-conductive state. This can befacilitated by increasing the concentration or number of conductivefilaments near the surface portion of the matrix and/or configuring themto be have a selected conduction direction. The matrix can also includea doped conductive layer, which can be electrically insulated from theheat exchange material.

The heat exchange material can be configured to perform severaldifferent thermal functions. For example, it can be configured to notonly conduct heat but also to act as a heat sink by coupling with apassive heat sink, a phase change material or other heat storage meansknown in the art. The phase change material can be a polymeric materialwhich can infill the cellular or other portions of the foam structure.The matrix can also be configured to function as a heat sink through theuse of active heat sinks such as thermal siphons or cooling channels ora combination of both.

In an exemplary embodiment of a method of using the matrix fordelivering energy to tissue, tissue is engaged with an electrosurgicalenergy delivery surface including a matrix comprising a positivetemperature coefficient of resistance (PTC) material and a heat exchangematerial disposed within an interior of the matrix. The energy deliversurface is then used to deliver Rf energy to tissue to ohmically heattissue in a target tissue volume. The delivery of Rf energy to thetissue is modulated utilizing the heat exchange material to exchangeheat with the PTC material to cause rapid switching of the PTC materialbetween substantially conductive and substantially non-conductivestates. This results in the production of a substantially uniformthermal effect in the target tissue volume as well as the prevention ofelectrical arcs in tissue and/or tissue charring due to one or more ofarcing, tissue desiccation or overheating of tissue. Such thermaleffects can include collagen and other protein denaturation and thegeneration of tissue welds and seals including high strength weldsformed in part formed by the fusion of the denatured collagen.

The switching process can be configured to not only produce a uniformthermal effect in tissue but also serve to substantially prevent orreduce charring and/or electrical arcing into tissue. This is achievedbecause before the tissue is heated to level at which charring andarcing can occur, the matrix is able to locally sense thetemperature/resistance of a given tissue portion via thermal conductionthrough the matrix and then rapidly switch to a non-conductive state tocease the delivery of Rf energy and thus ohmic heating of that portion.When the tissue cools down, the matrix is then able to rapidly switchback to a conductive mode. This process allows for the production oftissue welds and seals in a target tissue volume containing a number ofdifferent types of tissue, for example, fascia, muscle, and other softtissue because the matrix is able to spatially sense thetemperature/resistance of each tissue type in contact with the deliverysurface and then spatially modulate the delivery of energy accordingly.In particular, it allows for the generation of high strength fluidicseals in blood vessels including arteries by spatially modulating thedelivery of energy to denature and then fuse the collagen in the vesselwall.

Particular embodiments provide a polymeric PTC-based electrosurgicaldevice configured to disallows I²R heating at electrosurgical energyparameters. In other words, such PTC material cannot heat itself atelectrosurgical energy delivery parameters. Related embodiments providea polymeric PTC material that can switch extremely rapidly between a lowbase resistance value and a very high resistance value, for example,many times per second. Such embodiments can include a PTC-basedthermistor for use in very rapid repetitive use (i.e., switching) suchas is necessary in telecommunications devices and equipment. Still otherrelated embodiments provide a polymeric PTC based electrosurgicalsystems that can spatially modulate current flow across a tissuecontacting of an electrosurgical devices such a forceps. Such system canutilize polymeric PTC materials configured to allow for high spatialresolution, herein called pixelated resolution, for highly localizedswitching across a surface of the PTC material that engages tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments of the invention and are incorporated inand constitute a part of this disclosure. The embodiments in thedrawings taken together with the description serve to explain theprinciples of the present invention.

FIG. 1A is an exploded schematic view of a prior art current-limitingdevice with a polymeric PTC body sandwiched between first and secondelectrodes.

FIG. 1B is a schematic view of a prior art current-limiting device orthermistor in a circuit diagram.

FIG. 1C is a schematic view of a prior art constant temperature heatingdevice in a circuit diagram.

FIG. 2 is an exemplary temperature-resistance curve of a polymeric PTCcomposition.

FIG. 3 is a perspective view of a surgical forceps with anelectrosurgical jaw structure that carries the PTC sensing surface ofthe invention.

FIG. 4 is an enlarged view of the PTC sensing surface of the jaws as inFIG. 3 taken along line AA of FIG. 3.

FIG. 5 is a perspective view of an alternative high-compressionelectrosurgical jaw structure that carries the PTC sensing surface ofthe invention.

FIG. 6 is an enlarged view of the PTC sensing surface of the jaws ofFIG. 4 taken along line AA of FIG. 5.

FIG. 7 is a schematic view of the PTC sensing surface with passivecooling component taken along line A-A of the electrosurgical jawstructure of either FIG. 4 or FIG. 6.

FIG. 8 is a schematic view of the PTC sensing surface of FIG. 7 furtherdepicting a method of the invention in interacting with tissue.

FIG. 9 is a schematic view of an alternative PTC sensing surface withspaced apart heat diffusing elements.

FIG. 10 is a view of forceps used in neurosurgery that has novel PTCenergy-delivery surfaces.

FIG. 11 is an enlarged view of an alternative PTC surfaces similar tothat of FIG. 10.

FIG. 12 is an enlarged view of an alternative PTC surfaces similar tothat of FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

Operational principles of polymeric PTC devices for sensing surfaces.Various embodiments of the invention provide polymeric compositions thatexhibit positive temperature coefficient of resistance (PTC or PTCR)effects. Embodiments also provide devices and systems which utilizethose PTC compositions in various applications including for example,electrosurgical, telecommunication, sensing and related applications.Particular embodiments provide PTC-based electrosurgical instrumentssystems and devices configured to provide: (i) high spatial resolutionin thermal sensing functionality and (ii) contemporaneous pixelatedcurrent-limiting functionality. Embodiments of such PTC based systemsherein are referred to at times as “dual function” PTC systems and/ordevices.

Describing a material as having a positive temperature coefficient (PTC)of resistance simply means that the resistance of the material increasesas temperature increases. Many metal-like materials exhibit electricalconduction that has a slight positive temperature coefficient ofresistance. (Materials that conduct like metals have the lowestresistivity of all non-superconducting materials, wherein resistivitygenerally falls in the range of 1-100 μΩ-cm.). In such metal-likematerials, the PTC's variable resistance effect is characterized by agradual increase in resistance that is linearly proportional totemperature—that is, a linear PTC effect.

A “nonlinear” PTC effect is exhibited by certain types of polymermatrices that are doped with conductive particles. These polymer PTCcompositions have a base polymer that undergoes a phase change or glasstransition temperature T_(G), wherein the PTC composition has aresistance that increases sharply or otherwise non-linearly over anarrow temperature range (see FIG. 2). Many embodiments of the inventionrelate to the use of such non-linear PTC materials.

For ease of discussion, an explanation will now be provided of variousterms relating to operational characteristics of polymeric PTCcompositions. These terms have the meaning given unless otherwiseindicated in the specification:

T_(S): Switching temperature: this is temperature at which thecomposition exhibits a very large nonlinear PTC effect; that is it will“trip” to very high current-limiting resistivity from low quiescentresistivity;

T_(G): Glass transition temperature: this is the temperature at whichpolymeric base material transitions from a glass state to a rubberystate;

T_(M): Melt temperature: this is the temperature at which a crystallinematerial transitions from a nonflowable state to flowable state;

I_(Hold): Hold current: this is maximum current a PTC composition willsustain for a selected time interval at a certain temperature (e.g., 20°C.);

I_(Trip): Trip current: this is the minimum current that will cause aPTC composition to reach its switching range to become non-conductive ata certain temperature (e.g., 20° C.);

V_(Max): Maximum voltage: this is maximum voltage a PTC compositionwithstands without damage;

I_(Max): Maximum current: this is the maximum current a PTC compositionwithstands without damage;

R_(IL): This is the minimum resistance of a PTC composition in aninitial quiescent state;

R_(AT): This is the maximum resistance of a PTC composition innon-tripped state after cycling between quiescent and operationalstates; and

P_(D)Max: This the power dissipated from a PTC composition when trippedat its switching range.

When describing properties of the base polymer used in a PTCcomposition, it is useful to further explain the terms glass transitiontemperature (T_(G)) and melting temperature (T_(M)). Glass transitiontemperature is not the same as melting temperature. A transition at TMoccurs in crystalline polymers when the polymer chains fall out of theircrystalline phase, and become a disordered deformable or flowable media.A glass transition at T_(G) is a transition which occurs in amorphouspolymers (i.e., polymers whose chains are not arranged in orderedcrystals) where the polymer transitions from glassy state in which it isrelatively hard and rigid to a rubbery state. A glass transitiontemperature (T_(G)) in a crystalline polymer is herein loosely definedas a temperature point where the polymer experiences a significantchange in its mechanical and/or rheological properties—such as a largechange in its Young's modulus (also known as modulus of elasticity). TheT_(G) is the temperature at which the polymer structure turns “rubbery”upon heating and “glassy” upon cooling. Crystalline polymers also gothrough a stage of becoming leathery before becoming rubbery. There is aloss of stiffness (modulus of elasticity) in both of these stages. Suchcrystalline polymers or domains have a sharp, defined melting pointT_(M). In contrast, while an amorphous polymer is in a solid or rigidstate below T_(G) and rubber above that temperature, its transition frombeing rigid to flowable occurs over a wide temperature range as opposedto distinct temperature such melting point temperature for crystallinematerial.

A discussion will now be presented of the thermodynamic equations andrelations useful in understanding the operating characteristics of PTCmaterials. The temperature-induced variable resistance of a polymer PTCcomposition when used in a prior art current-limiting application isbased on an overall energy balance—and can be described by Equation (1)below. It is useful to describe the basic thermal/resistance propertiesof a polymeric PTC composition, to thereafter explain how non-linear PTCeffects and rapid switching are achieved in a “system” corresponding tothe invention.mC _(p)(ΔT/Δt)=I ² R−U(T−T _(a))  (1)

Wherein:

m=mass of the PTC composition

C_(p)=specific heat capacity of the PTC composition (at a constantpressure)

ΔT=change in temperature of the PTC composition

Δt=change in time

I=current flowing through the PTC composition

R=resistance of the PTC composition

U=overall heat-transfer coefficient

T=temperature of the PTC composition

T_(a)=ambient temperature

In equation (1) above, the current flowing through the PTC compositiongenerates heat at a rate equal to I²R. All or some of the heat can besubtracted by interaction with the environment at a rate described bythe term U(T−T_(a)). Any heat not subtracted by environmentalinteraction raises the temperature of the PTC composition at a ratedescribed by the term:mC _(p)(ΔT/Δt)  (2)

To keep Equation (1) as simple as possible, assume a uniform temperatureacross the polymeric PTC composition.

If the heat generated by the polymeric PTC composition and the heatsubtracted to the operating environment are in balance, T/t goes tozero, and Equation (1) can be rewritten as:I ² R−U(T−T _(a))  (3)

Under certain operating conditions, the heat generated by the PTCcomposition and the heat lost by the device to the environment can be inbalance at a relatively low temperature—for example, Point A in FIG. 2.If the current flow (I) through the PTC composition increases and theambient temperature remains constant, the heat generated by the PTCcomposition increases, and the temperature of the PTC composition alsoincreases. But if the increase in current is not too large, all thegenerated heat can be lost to the environment, and the PTC compositionwill stabilize according to Equation (3) at a higher temperature, suchas Point B in FIG. 2.

If the ambient temperature (or tissue engaged by the PTC composition)increases instead of the current, the PTC composition will stabilizeaccording to Equation (3) at a higher temperature (possibly again atPoint B in FIG. 2). Point B in FIG. 2 can also be reached as a result ofan increase in current (I) and an increase in ambient temperature.Further increases in either or both of these conditions will cause thePTC composition to reach a temperature T_(S) at which the resistancerapidly increases (e.g., Point C in FIG. 2).

Any further increase in current or ambient temperature will cause thePTC composition to generate heat at a rate greater than the rate atwhich heat can be lost to the environment, causing the PTC compositionto heat up rapidly. At this stage, large increases in resistance occurwith small changes in temperature. In FIG. 2, this occurs between PointsB and C, and this vertical or “square” portion of the curve defines theoperating region of the PTC composition in its tripped state. The largechange in resistance causes a corresponding decrease in current flow inthe circuit.

Because the temperature change between Points B and C in FIG. 2 is verysmall, the term (T−T_(a)) in Equation (3) can be replaced by theconstant (T_(S)−T_(a)), where T_(S) is the operating (current-limiting)temperature of the device. Then Equation (1) can be rewritten as:I ² R=V ² /R=U(T _(S) −T _(a))  (4)

Because U and (T_(S)−T_(a)) are now both constants, Equation (4) reducesto I²R=constant; that is, the device now operates in a constant powerstate. Expressing this constant power as V²/R emphasizes that, in thetripped state, the PTC composition resistance is proportional to thesquare of the applied voltage. This relation holds until the deviceresistance reaches the upper “square” region of the curve (Point C inFIG. 2).

For a PTC composition that has tripped, as long as the applied voltageis high enough for the resulting V²/R to supply the U(T_(S)−T_(a)) loss,the PTC composition will remain in the tripped state; that is, the PTCcomposition will remain non-conductive. When the voltage is decreased tothe point at which the U(T_(S)−T_(a)) loss can no longer be supplied,the PTC composition will “reset” or return to its quiescent baseresistance.

In the context of FIGS. 1B and 1C, it can be understood how the aboveequations describe the operation of a PTC composition in acurrent-limiting device (cf. FIG. 1B) and a constant temperature heatingdevice (cf. FIG. 1C).

Various embodiments of the invention provide systems and devices thatallows for a very rapid bi-directional switching (Δt) along theresistance-temperature curve of FIG. 2 (indicated by arrow 100). Manyembodiments provide polymeric PTC compositions that exhibits aresistance-temperature curve with a high degree of “squareness” at itsT, (at Point C in FIG. 2). Specific embodiments provide a “system” thatcombines a passive heat exchange component within the polymeric PTCcomposition to optimize heat subtraction from matrix 50, which relatesto “U”—the overall heat-transfer coefficient in the equation:mC _(p)(ΔT/Δt)=I ² R−U(T−T _(a))  (5)

In other words, referring to the exemplary jaw structures of FIGS. 3-6,the heating of the PTC matrix 50 can be entirely limited to externalheating of the matrix surface by engaged tissue T when the jaw includesa heat exchange component 60 which can comprise a heat exchange material60. In various embodiments, heat exchange component 60 can comprise anypassive or active means for one or more of the rapid subtraction,diffusion, or transfer of heat from an electrosurgical tissue-engagingsurface that utilizes a PTC material to sense tissue temperature whilemodulating ohmic heating in the engaged tissue. Further, heat exchangecomponent 60 can comprise a number of heat exchange materials known inthe art including, without limitation, heat subtraction materials whichcan in turn include without limitation metals, graphite structures, heatpipes or thermosiphons, phase change materials, nano-materials,refractory materials, liquids and the like. For ease of discussion heatexchange component 60 will now be described as a heat subtractioncomponent 60, but other embodiments are equally applicable In variousembodiments, heat subtraction component 60 is configured to very rapidlydiffuse away or otherwise transfer or dissipate heat conducted to thetissue-engaging surface that comprises a PTC sensing device or otherwiseincludes PTC materials.

A discussion will now be presented of the uses of various embodiments ofPTC compositions in electrosurgical devices and related surgicalapplications. FIG. 3 illustrates an exemplary embodiment of aforceps-type electrosurgical instrument 90 that can use a PTRC basedmatrix 50 to modulate or the control delivery of radio-frequency (Rf)energy to tissue for one or more electrosurgical procedures such astissue welding. It should be appreciated that forceps 90 is butexemplary instrument and other electrosurgical instruments and devicesknown in the art such as a scissors, scalpels, resection tools, tissueablation instruments and the like. Forceps 90 includes a working end orelectrosurgical jaw structure 100A has tissue-engaging surfaces 106A and106B in first jaw element 112A and second jaw element 112B that close orapproximate about axis 115 that is straight or curved. It should beappreciated that in various embodiments, the jaw elements can be of anycurved or straight shape (or a combination of both) configured for openor endoscopic surgeries with scissors-type actions or with one or morecam mechanism as is known in the art. The jaws also can carry a slidingcutting blade as described in U.S. patent application Ser. No.10/443,974, filed May 22, 2003 (Docket No. 021447-000590US) titledElectrosurgical Working End with Replaceable Cartridges, and ProvisionalU.S. patent application Ser. No. 60/537,085 filed Jan. 16, 2004 (DocketNo. SRX-028) titled Electrosurgical Working End with ReplaceableCartridge. FIG. 4 graphically illustrates the opposing jaws 112A and112B engaging tissue T, with an electrode 110 having an exposed surface.

FIGS. 5 and 6 depict an alternative embodiment of a working end with jawstructure 100B that can carry the same PTC matrix 50 and heatsubtraction component 60 as the forceps-type jaw structure of FIGS. 3and 4. The jaw structure 100B of FIG. 5 carries a blade for transectingthe welded tissue. FIG. 6 illustrates a cross section of the upper andlower jaws 112A and 112B of FIG. 5 with a central blade slot 118 forreceiving the slidable blade member 120. On either side of the bladeslot 118, the jaw bodies carry variable resistive matrices 50 (and 50′)that are similar (or identical) to the matrices depicted in FIGS. 3 and4. In the exemplary embodiment of FIG. 5, the lower jaw 112B has amatrix 50′ with electrode 110 being exposed in the center of the jaw'sengagement surface 106B with a portion of the PTC matrix 50′ extendinglaterally on either side of blade slot 118 as well as within theinterior of the jaw. As can be seen in FIG. 5, matrix extends in a“U”-shape around the end of blade slot 118 to allow welding of engagedtissue around the end of a welded and transected tissue region.

In many embodiments, the working ends 100A and 100B of FIGS. 3-6 areconfigured to function to modulate Rf energy application to tissue inmultiple potential current paths as depicted, for example, in FIG. 6.FIG. 6 illustrates the working end 100B engaging tissue with a graphicaldepiction of the potential Rf current paths P in tissue and acrossregions of the PTC matrices.

In one preferred embodiment, illustrated in FIGS. 3-6 and schematicallyin FIG. 7, a system of the invention combines a polymeric PTC matrix 50with a heat subtraction material 60 having a high thermal diffusivityproperty. It is believed that certain graphite foams offer the highestthermal diffusivity of any known material, and is suited for heatsubtraction from engagement surface 106A. The term “thermal diffusivity”defines a measure of how quickly heat is transported through thematerial compared with how quickly the material absorbs the heat.Thermal diffusivity thus is defined as thermal conductivity divided bythe product of density and specific heat. Suitable graphite foamsinclude POCOFOAM commercially available from Poco Graphite, Inc., 300Old Greenwood Rd., Decatur, Tex. 76234. This material has a very highthermal conductivity, coupled with low density and low specific heat,resulting in high thermal diffusivity.

Carbon foam materials are composed of amorphous carbon and havedensities ranging from 0.12 to 0.50 g/cm³. Generally, carbon amorphousstructures have good thermal insulating properties with thermalconductivities less than 10 W/m K. However, PocoFoam™ is derived frommesophase pitch, an intermediate phase in the formation of carbon frompitch that when heated above 2000° C. forms graphite. This precursormaterial, combined with an innovative production method, produces amaterial with very high thermal conductivity. It differs fromconventional carbon foams in that the ligaments making up thehoneycomb-like structure of the foam are of a highly aligned andcrystalline-like structure rather than being strictly amorphous as inother carbon foams. The difference in such molecular alignments givesthis carbon foam its very high thermal conductivity. Another advantageof this foam, compared with other materials that also have high thermalconductivities such as carbon-carbon composites and graphite fibers, isthat this preferred foam conducts heat in all directions. Composites andfibers only conduct well in the direction of the fiber.

2. Method of interaction enabled by PTC devices with sensing surfaces.The need for a polymeric composition that exhibits a highly nonlinearPTC effect and well as a repeatable, very fast switching time arose fromnew inventions in the field of electrosurgery (see, e.g., the authors'co-pending U.S. patent application Ser. No. 10/032,867). In deliveringenergy to biological tissue to perform tissue-welding procedures, it wasdetermined that a variable resistive material was needed that couldaccomplish new types of thermal and electrical interactions with tissue,viz., the combination of a temperature sensing function and acurrent-limiting function for modulated I²R (ohmic) tissue heating.Further, it was determined that the variable resistive PTC compositionwould need to be highly sensitive in functioning in a thermal sensingrole—to thereby provide very high spatial resolution to the thermalsensing function and to provide contemporaneous application ofelectrical energy with the same very high spatial resolution. By theterm spatial resolution, it is meant that the variable resistive PTCmaterial provides, effectively, a “pixelated” operating surface whereinsome pixels (or spatial regions) of the PTC surface are above itsswitching temperature, T_(S), while adjacent pixels or regions are belowits T_(S). This material property is achieved by the development of apolymer body (or surface layer) exhibiting a highly nonlinear PTC effectand a very rapid and localizable switching speed, as described above. Inone embodiment, the switching speed at a local region of the engagementsurface of the PTC device is greater than 10 Hz. More preferably, theswitching speed in greater than 20 Hz, and still more preferably isgreater than 30 Hz. In one embodiment, the PTC matrix is configured tobe incapable of I²R heating when engaging tissue and has an internalresistance of an order of magnitude less than the resistance of engagedtissue. More preferably, the PTC matrix has an internal resistance oftwo orders of magnitude less than the resistance of engaged tissue; andstill more preferably the PTC matrix has an internal resistance of threeorders of magnitude less than the resistance of engaged tissue.

Various embodiments of the invention are well suited to electrosurgicalapplications in part, based on two considerations. First is the factthat the target biological tissue exhibits properties that arenon-uniform and dynamic during the process of I²R (ohmic) heating.Therefore, embodiments of an electrosurgical instrument having a PTCmatrix are desirably able to thermally sense temperature non-uniformityacross the spatial geometry of a tissue-engaging surface 106A of the PTCbody—in effect a pixelated sensing function. Second, the PTC matrixdesirably exhibits corresponding non-uniform heating across thepixelated PTC surface correspond able to the sensed tissue temperatures,resulting in dynamic, non-uniform, pixelated resistivity. In use theseproperties can be applied to allow the PTC surface to apply pixelatedI²R or ohmic heating within the engaged tissue regions to heat them to atargeted temperature to achieve a desires tissue effect such as uniformprotein denaturation, tissue welding, high strength tissue welding, etc.Further, the PTC matrix can adjust in resistivity very rapidly toprevent arcing and tissue charring at the interface of the tissue andthe electrosurgical surface.

FIGS. 7 and 8 schematically depict a portion of a jaw structure (as inFIGS. 3-6) wherein the arrangement of the polymeric PTC composition 50in relation to the subject material (biological tissue T or otherwise)differs from conventional uses of PTC materials as depicted in FIGS. 1Band 1C. In FIGS. 6 and 7 it can be seen that the PTC composition 50 canbe adapted to directly engage and interact with surface 106A of thesubject material T, without any interposed electrically insulativecoating (cf. FIGS. 1B and 1C). In use, such embodiments allow for thesurface 106A or the jaw surface of another electrosurgical device tocontemporaneously interact with the subject material 110, in both heatsensing and I²R heating modes of operation.

Accordingly, various embodiments of the invention provideelectrosurgical methods for treating tissue wherein a surface of anelectrosurgical devices having a PTC composition 50 described hereincontemporaneously interacts with the subject material 110, using bothheat sensing and I²R heating functionality. One such embodiment shown inFIG. 7. comprises (i) providing a polymeric PTC composition thatsubstantially disallows I²R heating and thus prevents a nonlinear PTCeffect therein; (ii) engaging the PTC composition with the subjectmaterial or tissue T; (iii) coupling a voltage source 150A to the PTCcomposition and the subject material in a series circuit to causecurrent flow resulting in an I²R heating interaction within the subjectmaterial; (iv) allowing heat within the subject material or tissue T totransfer to and interact with PTC composition 50 to cause a nonlinearPTC effect therein to modulate I²R heating in the subject material, and(iv) allowing the heat subtraction component 60 to rapidly diffuse heataway from the PTC material's surface 106A.

Various embodiments of the invention utilizing PTC materials can beconfigured to have a functionality useful for producing selected thermaleffects in material including uniform heating of materials. Specificembodiments can be configured to provide uniform heating of materialsthat have non-uniform or dynamic electrical properties, such asbiological tissue, as depicted in more detail in FIG. 8. In thisembodiment, heat subtraction component 60 comprises a graphite foam 60described herein but other heat subtraction components are equallyapplicable. In FIG. 8, the tissue's electrical non-uniformity isindicated graphically by three hatching shades. In such electrosurgicalinteraction with tissue, an alternating current is used. It can beunderstood that voltage source 150A will apply current through theseries circuit and in a microcurrent path P₁ in tissue that defines theleast resistance through the tissue. The alternating current along pathP₁ in the tissue will cause I²R heating therein. The localized ohmically(I²R) heated tissue indicated at 165 that engages region 170 of PTCcomposition 50 will then be passively heated by conduction from thetissue. In turn, that region 170 of the PTC composition functions as asensor and responds at about its T_(S) to contemporaneously becomehighly resistive. At the same time adjacent tissue 165′ that is mostconductive engages PTC region 170′ that is also in its low resistancestate. The highly localized heating of PTC “pixel” indicated at 165 thenwill cause microcurrent paths to shift to the more conductive path, P₂.As any surface pixel of the PTC material is elevated in temperature,graphite foam 60 very rapidly diffuses the heat thus causing the pixelto switch back to its conductive state—unless still heated by ohmiceffects in the adjacent tissue.

Embodiments of the system allows for highly dynamic, spatial resolutionof pixelated resistivity and current flow across the surface of the PTCcomposition 50. Further, the graphite foam, operating as a heatsubtraction component, will rapidly diffuse heat to thus make the PTCdevice switch faster.

Still referring to FIG. 8, in particular embodiments for fabrication ofPTC materials, the polymeric PTC material 50 is melted so as to flowinto the open cells of the graphite foam 60. This results in a couplingbetween the high surface area of the foam and the polymer that isextremely well suited for thermal conduction. In this embodiment, asubstantially thick layer of PTC indicated at 180 is provided at thesensing or engagement surface 106A, since the graphite is electricallyconductive and needs to be maintained inward of the surface. In anothermore preferred embodiment, the graphite foam is coated with a coatingthat is substantially thermally conductive but electricallynon-conductive. A thin polymer can serve this purpose. In thisembodiment, the layer of PTC material 180 would remain at the sensing orengagement surface, but the graphite foam could extend closer to thetissue-engaging surface.

In another more preferred embodiment of PTC system 185 illustrated inFIG. 9, the graphite foam 60 can be formed in pixels or posts 188 thatare spaced apart in the polymeric PTC material 50. In this embodiment,it can easily be understood that the heat diffusion will be induced tobe in the direction of arrows generally orthogonal to the plane of thePTC sensor surface 106A. This embodiment will thus prevent the lateraldiffusion of heat which in turn will enhance spatial resolution of thePTC material's switching capabilities.

3. Methods of fabrication of polymeric PTC devices for sensing surfaces.A discussion will now be presented of methods of fabrication of variousembodiments PTC materials. These methods are exemplary and other methodsknown in the art may be used. Various embodiments of the polymeric PTCcompositions described herein comprise a matrix of a base polymer 190with electrically conductive particles 192 dispersed therein as is knownin the art. The base polymer component 190 can be a crystalline orsemi-crystalline polymer such as in the polyolefin family and moreparticularly a polyethylene. Suitable polyethylenes include withoutlimitation HDPE, LDPE, MDPE, LLDPE. The base polymer component 190 alsocan be a copolymer of at least one olefin and one or more other monomersknown in the art that can be co-polymerized with the olefin. Othersuitable base polymer component include without limitation polyamide,polystyrene, polyacrylonitrile, polyethylene oxide, polyacetal,thermoplastic modified celluloses, polysulfones, thermoplasticpolyesters (e.g., PET), poly(ethyl acrylate), or poly(methylmetbacrylate). Other suitabel co-polymers include without limitation,NYLON, fluoropolymers such as polyvinylidene fluoride and ethylenetetrafluoroethylene, or blends of two or more such polymers. Inpreferred embodiments, the polymer base component 190 can be anyhigh-density polyethylene, low-density or medium-density polyethyleneavailable from Dow Chemical, Union Carbide or Dupont-MitsuiPolychemicals Co., Ltd., all of which make suitable polyethylenes. Theparticular polyethylene chosen can be selected for its density and meltflow viscosity. For example, materials with lower melt flow viscocitycan be chosen to improve the melt flow of melted PTC material 50 intofoam 60 as is described herein. Improved melt flow of material 50 intofoam 60 in turn improves the thermal conductivity between the twomaterial as is also described herein.

It is generally has been determined that the T_(S) of a polymeric PTCcomposition is within the region of the glass transition temperature(T_(G)), which is well below the melt temperature (T_(M)) of thecrystalline polymer. If the thermal expansion coefficient of the polymeris sufficiently high above the T_(G), a highly non-linear PTC effectwill occur. Preferably, base polymers 190 has a high degree ofcrystallinity but it can also be semi-crystalline. However, in order tofabricate a polymer composition with a highly nonlinear “square” PTCeffect, it is preferable that the polymer has a T_(G) in the temperaturerange of 70° C. to 300° C.; though, other range for T_(G) may also beused.

The conductive particles 192 can be carbon particles. Other particletypes include without limitation, silver, tin, nickel, gold, copper,platinum, palladium, magnesium, aluminum, molybdenum, tungsten,tantalum, zinc, cobalt or a combination thereof.

The conductive particles are mixed into a melt-state polymer until theparticles are well dispersed. By any technique known in the art, themixing is accomplished in a system that provides a temperature higherthan the melting point of the polymeric base 190. In mixing the polymerbase 190 with the particles 192, and optional additives described below,the objective of mixing is to create a uniform distribution of particleswithin the matrix. For example, the mixing temperature and time must beproperly controlled so that the conductive particles will uniformlycreate conductive paths within the matrix as the PTC body operates. Anexcessive mixing time may cause a separation between conductiveparticles resulting in non-uniform conductive paths as the polymercomponent polymerizes from a liquid into a solid. Non-uniform formationof conductive paths is undesirable because it can result in internalarcing during its operation.

The thermoplastic polymer base 190 can carry other additives known inthe art, such as flame retardants or anti-arcing compositions, ananti-oxidizing agent (magnesium oxide or titanium oxide), ananti-ozonizing agent, a cross-linking agent or any combination thereof.In the fabrication process, the mixture can also be treated with variousprocesses (e.g., gamma, UV irradiation etc.) to cross-link the polymeror co-polymers of the matrix. However, it has been found that it is notnecessary to cross-link the polymer base material 190 to provide a fullyfunctional PTC composite.

The polymeric PTC composition thereafter can be pressed into sheetmaterial for further processing. For example, foil electrodes can beattached on either side of the PTC sheet for making a thermistor. Whenused as a thermal sensor or constant temperature heater, the PTCcomposition can be molded or extruded in any suitable shape.

Many embodiments of the invention employ the use of graphite foams(described herein) for enhancing the performance of the PTC systems fortissue sealing. However, it will also be appreciated that variousembodiments of the invention also contemplate other heat subtraction andheat sinks technologies known in the art which can be used in place ofor in conjunction with graphite foam. It further can be seen thatpassive or active systems for heat diffusion will work best ifdistributed throughout the polymeric PTC material.

Thus the scope of the invention includes any passive heat sink coupledto the PTC composition, such as any thermally conductive heat exchangedevices.

The scope of the invention also includes oriented thermally conductivefibers or filaments (e.g., carbon fibers) that are molded directly intothe polymeric composition to diffuse heat, either uni-directionally,bi-directionally or omni-directionally.

The scope of the invention includes any active heat sinks in the form ofcooling channels, heat pipes or thermosiphons and the like as known inthe art of thermal management.

The scope of the invention also includes any active cooling systems ofthe types disclosed in a related electrosurgical instrument inco-pending U.S. patent application Ser. No. 10/781,925 filed Feb. 14,2004 (Docket No. 021447-000810US) titled Electrosurgical Instrument andMethod of Use.

4. Tissue interactions with related PTC devices having heat diffusivitycomponent. A discussion will now be presented of methods of usingembodiments PTC based electrosurgical instruments and devices includingtissue interactions. Embodiments of the invention can be configured toutilize PTC materials to provide several thermal effects including ohmicheating of tissue, denaturation of proteins in tissue and the welding oftissue. In particular various embodiments can utilize ohmic heating torapidly denature proteins in a target tissue volume. This denaturedcollagen can then be fused (e.g., by the application of force ) rapidlyform a new collagen matrix. Thus, in use, such ohmic heating allows forthe creation of welds or seals in tissue that have high strengthimmediately post treatment because the formation of the new collagenmatrix from the denatured proteins adds a high strength collagencomponent to the strength of the seal, in essence using the natural highstrength material of collagen to form the seal. Such methods areparticularly suitable for forming high strength welds in various bloodvessels including arteries as well as thick tissues, tissue bundles andother collagen containing materials. In the case of arterial welds,embodiments of such method allows for the rapid creation of not only ahigh strength weld, but a high strength fluidic seal which will not leakfrom arterial pressure.

In other embodiments, the PTC based electrosurgical devices can beconfigured for using conductive heating as opposed to ohmic heating asmeans to weld or seal tissue. While high strength welds are desirable ina number of surgical applications, there remain other situations inmicrosurgeries, neurosurgeries, sealing fragile veins, sealing thinmembranes and the like wherein high strength welds are not critical. Insome of these sealing applications, the use of conductive heating(contrasted with ohmic heating) may be desirable. For example, inneurosurgery it is often necessary to seal very small vessels that carrylimited pressures. Here the principal objectives are prevention ofsticking and collateral thermal or other damage.

FIG. 10 illustrates an embodiment of a forceps 200 configured for use inneurosurgery and related applications. The forceps 200 include tines orjaw elements 202 a and 202 b. In the embodiment of FIG. 10, one or bothengagement surfaces 205A and 205B can comprise in part a polymeric PTCcomposition 250 that is capable of I²R (Joule) internal heating—which isunlike all previous embodiments. Again, the PTC composition 250 iscarried in the voids of a graphite cellular material 60, such asPOCOFOAM™. The graphite foam can extend to the tissue-engaging surface.In operation, it can be understood that the PTC composition can beselected to provide a selected temperature for sealing a very thintissue. The graphite foam will then function to provide very uniformtemperature across the engagement surfaces, which will insure that thethin tissues are heated uniformly and prevent hot spots, which canresult in sticking.

In a closely related embodiment illustrated in FIG. 11, the PTCcomposition 250 can carry microencapsulated phase change materials(PCMs) 255 as disclosed in detail in U.S. Provisional Patent ApplicationSer. No. 60/558,672 filed Apr. 1, 2004 (Docket No. SRX-030) titledSurgical Sealing Surfaces and Methods of Use. In that disclosure, theinvention provided an energy modulating surface for interfacing withtissue. The tissue-engaging surface can be in a surgical probe or jawstructure. The energy modulating surface uses PCMs to protect theengaged tissue from excessively high local temperatures that result inchar and sticking through the physical phenomenon of the absorption ofthe PCMs latent heat of fusion. The phase change material is capable ofpractically instantaneous localized absorption of the material's latentheat to stabilize tissue temperature at the probe-tissue interface. Thetemperature modulation can occur in a localized manner, or “pixelated”manner, across the surface of the energy modulating material. The energymodulating surface can increase the strength of tissue welds, inaddition to preventing charring and sticking.

In FIG. 12, a final embodiment for prevention of tissue sticking isshown which is the same as described in FIG. 11 with the addition ofthin surface layer 275 (exploded view) of a non-conductive polymer suchas a silicone or the like. This polymer layer can be configured to allowsubstantially all electrosurgical and/or thermal energy to be conductedtherethrough, but will prevent electrical arcs at the interface of thetissue and the electrosurgical surface as well as limiting tissueadherence and sticking to the surface. It should be appreciated that asimilar thin polymer layer 275 can be added to any of the surfaces ofFIGS. 3-9 wherein the polymer layer will not substantially hindercurrent flow to cause ohmic heating in the engaged tissue. Suchnon-conductive polymer surface layers can include a thin film materialthat is bonded to the electrosurgical surface or a flowable materialthat is polymerized and bonded in place after application to theelectrosurgical surface.

Embodiments of the invention further include any thermal energy deliverysurface for use in surgical sealing that carries a PCM material in apolymer sealing surface. Embodiments of the invention also encompassesany thermal energy delivery surface that carries oriented conductivegraphite or similar elements for optimizing performance by its thermaldiffusivity.

It should be appreciated that the system and electrode arrangement ofFIG. 6 can be utilized to provide thermal sensing and I²R heating of anyconductive subject material, such as metals, polymeric compositions,ceramic compositions, combinations thereof and the like.

Conclusion: The foregoing description of various embodiments of theinvention has been presented for purposes of illustration anddescription. It is not intended to limit the invention to the preciseforms disclosed. Many modifications, variations and refinements will beapparent to practitioners skilled in the art. Further, the teachings ofthe invention have broad application in the electrosurgical andlaparoscopic device fields as well as other fields which will berecognized by practitioners skilled in the art. Such fields can includewithout limitation various minimally invasive and endoscopic methodsincluding those in the areas of urological, gynecological, ENT, GI,dermatological, plastic surgery, oncological, orthopedic, dental andother medical fields known in the art.

Elements, characteristics, or acts from one embodiment can be readilyrecombined or substituted with one or more elements, characteristics oracts from other embodiments to form numerous additional embodimentswithin the scope of the invention. Hence, the scope of the presentinvention is not limited to the specifics of the exemplary embodiment,but is instead limited solely by the appended claims.

1. A matrix for an electrosurgical energy delivery surface, the matrixcomprising: a positive temperature coefficient of resistance (PTCR)material, the material having a substantially conductive state and asubstantially non-conductive state; and a heat exchange materialdisposed within an interior of the matrix, the heat exchange materialhaving a structure configured to provide directional thermal diffusivityfor exchanging heat with the PTCR material to cause rapid switching ofthe PTCR material between the conductive state and the non-conductivestate.
 2. The matrix claim 1, wherein the heat exchange materialconducts heat from the PTCR material to cause rapid switching of thePTCR material between the conductive state and the non-conductive state.3. The matrix claim 1, wherein the heat exchange material has auni-directional thermal diffusivity.
 4. The matrix claim 1, wherein thestructure is a cellular structure, a non-amorphous structure or acrystalline structure.
 5. The matrix of claim 1, wherein the matrix iscarried in a tissue-contacting surface of an electrosurgical device. 6.The matrix of claim 1, wherein the matrix is carried in at least one jawof an electrosurgical device.
 7. The matrix of claim 1, wherein the PTCRmaterial is electrically insulated from the heat exchange material. 8.The matrix of claim 1, wherein the heat exchange material comprises atleast one graphite element.
 9. The matrix of claim 1, wherein the atleast at a portion of the matrix comprises a graphite foam structure.10. The matrix of claim 9, wherein at least a portion of the graphitefoam structure is a cellular structure, an open cell structure, anon-amorphous structure or a crystalline structure.
 11. The matrix ofclaim 9, wherein the graphite foam structure comprises a plurality ofthermally conductive filaments.
 12. The matrix of claim 11, wherein atleast a portion of the thermally conductive filaments are oriented toconduct heat in a unidirectional, bi-directional, or omni-directionalmanner.
 13. The matrix of claim 1, wherein the heat exchange material iscoupled to a heat sink.
 14. The matrix of claim 1, wherein the heatexchange material comprises a phase change material.
 15. The matrix ofclaim 1, wherein the heat exchange material is a thermosiphon.
 16. Thematrix of claim 1, wherein the heat exchange material has anelectrically non-conductive polymer surface layer.
 17. A matrix for anelectrosurgical energy delivery surface, the matrix comprising: apositive temperature coefficient of resistance (PTCR) material, thematerial having a substantially conductive state and a substantiallynon-conductive state; and a non-conductive polymer layer disposed on theenergy delivery surface.
 18. The matrix of claim 17, further comprising:a heat exchange means for exchanging heat with the PTCR material tocause rapid switching of the PTCR material between the conductive stateand the non-conductive state.
 19. A method of applying controlled energyto treat tissue, the method comprising: engaging tissue with anelectrosurgical surface, the surface coupled to a matrix comprising apositive temperature coefficient of resistance (PTCR) material and aheat exchange material disposed within an interior of the matrix, thePTCR material having a substantially conductive state and asubstantially non-conductive state; delivering Rf current to tissue soas to ohmically heat tissue; and modulating the delivery of Rf currentto tissue wherein the Rf current flows at least partly through thematrix and the heat exchange material removes heat from the PTCRmaterial to substantially prevent tissue charring or arcing in tissue.20. The method of claim 19, further comprising: producing asubstantially uniform thermal effect in tissue.
 21. The method of claim20, wherein the substantially uniform thermal effect is at least one oftissue welding, tissue sealing, tissue seal strength, proteindenaturation or protein fusion.
 22. The method of claim 19, wherein heatis conducted uni-directionaly from the matrix.
 23. The method of claim19, wherein heat is conducted multi-directionaly from the matrix. 24.The method of claim 19, wherein the heat exchange material acts as aheat sink
 25. A method of applying controlled energy to treat tissue,the method comprising: engaging tissue with an electrosurgical energydelivery surface including a matrix of a positive temperaturecoefficient of resistance (PTCR) material and a heat exchange materialdisposed within an interior of the matrix; engaging tissue with thesurface; delivering Rf energy to tissue so as to ohmically heat at leasta portion of the engaged tissue; and utilizing the heat exchangematerial to remove heat from the PTCR material to cause rapid switchingof the PTCR material between substantially conductive and substantiallynon-conductive states.
 26. The method of claim 25, wherein the rapidswitching substantially prevents tissue charring or arcing in tissue.27. The method of claim 25, further comprising: utilizing the switchingto spatially modulate the delivery of Rf energy to tissue to produce asubstantially uniform thermal effect in tissue.
 28. The method of claim27, wherein the substantially uniform thermal effect is at least one oftissue welding, tissue sealing, tissue seal strength, proteindenaturation or protein fusion.
 29. A method of delivering energy totreat tissue, the method comprising: engaging tissue with anelectrosurgical energy delivery surface including a matrix comprising apositive temperature coefficient of resistance (PTCR) material and aheat exchange material disposed within an interior of the matrix, thePTCR material having a substantially conductive state and asubstantially non-conductive state; delivering Rf energy to tissue so asto ohmically heat tissue in a target tissue volume; spatially modulatingthe delivery of Rf energy to tissue utilizing the heat exchange materialto exchange heat with the PTCR material to cause rapid switching of thePTCR material between the substantially conductive and substantiallynon-conductive states; and producing a substantially uniform thermaleffect in the target tissue volume.
 30. The method of claim 29, whereinthe target tissue volume includes at least one of soft tissue, collagencontaining tissue, vascular tissue, muscular tissue, fascia tissue ordermal tissue.
 31. The method of claim 29, wherein the substantiallyuniform thermal effect is at least one of tissue welding, tissuesealing, tissue seal strength, protein denaturation or protein fusion.32. The method of claim 29, further comprising: spatially modulating thedelivery of RF energy to prevent at least one of charring or arcing intissue.
 33. The method of claim 29, further comprising: spatiallymodulating the delivery of RF energy to a blood vessel to create a highstrength fluidic seal in the vessel wall.